1. Field of the Invention
The present invention relates to an image processing apparatus and in particular to the art of determining an area in an image based on color information.
2. Related Art Statement
There is known an image processing device including a target-area determining means for determining a target area as one of a plurality of areas present in an object area, based on color information representing the color of each of a plurality of picture elements belonging to the target area. For example, a recent color-image printer has the function of cutting out, from an input image including a so-called "memory" color, an area having the memory color and converting the area (i.e., color-image data representing the area) in a special manner different from a common conversion manner, when producing an output image. A memory color is a color which human beings keep in their memory for a particular thing such as human being's skin or cherry's petal. However, generally, the difference between the memory color and the actual color of the thing is not negligible. Therefore, an output image is often better appreciated when a memory color, i.e., color which human beings keep in their memory is used than when an actual color is used. Accordingly, there has been developed the art of determining a target area having a memory color and converting color-image data representing the target area in a special manner (hereinafter, referred to as the "memory-color" conversion) different from a manner in which color-image data representing a non-target area other than the target area in the input image is converted.
Japanese Patent Application laid open for inspection purposes under Publication No. 5(1993)-324786 discloses an image processing device including a means for determining an area in an image based on color information. In this prior device, whether or not each of the picture elements of an original image belongs to a particular area to be subjected to a special color conversion is judged in the following manner: First, a primary target-area picture element is designated as a picture element to be subjected to the special color conversion, and a plurality of secondary target-area picture elements neighboring the primary element are determined according to a predetermined rule. Then, the respective colors of the primary and secondary elements are plotted in a color space, and are weighed by a probability distribution function (e.g., normal distribution function). Thus, a reference weighed distribution pattern is obtained. Concerning every picture element of the original image, a weighed distribution pattern is obtained in the same manner as described above, and is compared with the reference pattern. If the two patterns can be so similar as to be regarded as coinciding with each other, the picture element in question is judged as belonging to the target area.
However, in the above-identified prior device, a target area is determined based on only the color information representing the respective colors of the primary and secondary picture elements, and an inaccurate area may be determined as the target area. For example, when the prior device converts image data representing a color image including cherry's petals and a person wearing a cloth having a color similar to the color of the petals, the prior device may apply a special "memory-color" conversion to not only the petals but the cloth. In this case, the output image of the petals will be appreciated but the output image of the cloth will not be appreciated. In other words, the prior device cannot achieve both to satisfy human beings' sense to cherry's petals and to reproduce an accurate color of a cloth.